The present invention relates to latch assemblies which are provided with means for indicating whether the latch is in a locked or unlocked position. These latches are particularly useful for use on the exterior surfaces of aircraft where it is important that the latch present a flush surface with the aircraft body and also clearly indicate whether it is in the locked or unlocked position.
In general, latch assemblies of this type utilize an indicator or flag which remains in an up or protruding position while the latch is in the unlocked position. In the up position the flag is visible. When the latch assembly is in the locked position the indicator or flag is in the down or flush position and is not visible externally of the latch. The indicator or flag is generally provided in a contrasting color, so that individuals can readily ascertain whether or not the latch assembly is in a locked or unlocked position. This is especially critical in aircraft applications where an unlatched exterior door or hatch would be very hazardous during flight.
Due to the need for positive and secure latching on aircraft, the prior art latch assemblies utilize a rotary latching configuration. The rotor latch employs an irregular cam latching surface. As the irregular cam surface is rotated, it initially engages the surface to be latched. On continued rotation, the irregular cam surface draws the surface to be latched towards the center of the rotary latch assembly until it is rotated into the fully locked position. Prior art flags or visual indicators used on this type of latch may indicate that the latch is in the fully locked position when, in fact, it is in a condition of only partial locking. It is extremely important that the visual indicator or flag indicates a locked condition only when the latch is in a fully locked position.
Exemplary of such proir art latches is U.S. Pat. No. 3,503,642 issued to L. R. Poe on Mar. 31, 1970. This particular patent discloses a condition indicator utilizing a side arm catch and a complex spring actuated deflecting cam. The Poe patent also contains a "dead spot" where the latch may indicate that it is fully locked when, in fact it is not locked.
It would be desirable to have a latch mechanism which does not indicate a locked condition when the latch is only partially locked. The desired latch should indicate a locked condition only when the latch is fully locked and should indicate an unlocked condition when the latch is partially or fully unlocked. The indicator should also be simple in construction to provide a reliable indicator which is not subject to malfunction.